During chemical vapor deposition (CVD) processing, deposition gases are released inside a processing chamber to form a thin film layer on the surface of a substrate being processed. Unwanted deposition on areas such as the walls of the processing chamber also occurs during such CVD processes. Because the residence time in the chamber of individual molecules in these deposition gases is relatively short, however, only a small portion of the molecules released into the chamber are consumed in the deposition process and deposited on either the wafer or chamber walls.
The unconsumed gas molecules are pumped out of the chamber along with partially reacted compounds and reaction byproducts through a vacuum line that is commonly referred to as the “foreline.” Many of the compounds in this exhausted gas are still in highly reactive states and/or contain residues or particulate matter that can form unwanted deposits in the foreline. Given time, this deposition build-up of powdery residue and/or particulate matter presents a problem. First, the matter is often a substance that may present problems when the vacuum seal is broken and the foreline is exposed to ambient conditions during standard, periodic cleaning operations. Second, if enough of the deposition material builds-up in the foreline, the foreline and/or its associated vacuum pump may clog if it is not appropriately cleaned. Even when periodically cleaned, matter build-up interferes with normal operation of the vacuum pump and can drastically shorten the useful life of the pump. Also, the solid matter may backwash from the foreline into the processing chamber. This can adversely affect wafer yield.
This problem is particularly pronounced in the case of sub-atmospheric CVD (SACVD). In this case, a high TEOS flow creates residue that requires costly and time-consuming filtration. The filters clog frequently, requiring down-time to clean or replace the filters. Therefore, it is desirable to have an improved apparatus for trapping the residues that are byproducts of a CVD process, which can improve product yield, reduce the risk of pump damage, and reduce down-time in a semiconductor fabrication process.